AT524610B1 - Process for separating cellulosic fines from pulp suspensions and/or filtrates - Google Patents

Abstract

In a process for separating fines from filtrates from a paper, board, paperboard or pulp manufacturing plant and for reapplying the separated fines to a surface of paper, board or paperboard, at least the following steps are carried out: a) separating the fines from the filtrates with a size of less than 1200 μm (measured according to ISO 16065-1) and any other additives present, b) thickening of the fines separated from the same, c) optionally mixing the fines separated with other fines from a paper, cardboard - or pulp production, and/or microfibrillated cellulose (MFC), d) forming an aqueous suspension from the fines or optionally the mixture of fines from additives originating from paper or cardboard production e) optionally adding to the suspension other additives for the surface treatment of Paper or cardboard chosen of native and oxidatively degraded starch or calcium carbonate, f) homogeneous application of the suspension formed to a paper or cardboard surface in an amount between 0.5 and 30 g/m2, in particular 4 and 15 g/m2, the fines content in the suspension being below 99.5% of the dry matter contained in the suspension, preferably below 90.0% of the dry matter contained in the suspension, and g) drying the paper or cardboard and optionally simultaneous or subsequent pressing, calendering, coating with additives in a film - or sump size press or a spraying process or other coating units used in paper, cardboard and cardboard production.

Description

description

FIELD OF THE INVENTION

The present invention relates to a method for separating cellulosic fines from fibrous suspensions and/or filtrates of a paper or pulp plant and for simultaneously reapplying the separated cellulosic fines to and with a surface of paper, cardboard or paperboard Paper, board or paperboard produced by processes.

STATE OF THE ART

In paper, cardboard and cardboard production, as is well known, lignocellulosic starting material, in particular wood, which has been either mechanically or chemically digested in wood or pulp production, in particular with the addition of various chemicals, is used . The broken down and cleaned fibrous material is then mixed with other substances such as fillers such as calcium carbonate, starch, chemical additives and the like and then passed over a sieve and drained, whereupon, after the production of a sheet or a cellulose layer, sizing agents, Wet strength agents or other additives are added. With such a production process for paper, cardboard or cardboard as well as wood and pulp, care is taken in modern industry to keep the amount of necessary process water, residues and unused cooking chemicals or additives as low as possible by means of closed circuits, in order to be able to provide both a good mass and energy balance. If a fibrous material or a fibrous material suspension is cleaned and/or dewatered, in particular filtered on conventional filter systems, this filtrate contains not only a large number of chemicals and/or additives but also considerable amounts of fines that are suspended in these filtrates and which usually have a suitable process control via units such as disc filters, washing presses, flotation units and the like are kept in the process. At another point in the paper, cardboard and cardboard production, when the fibrous suspension is passed over the screen, the fibrous suspension is heavily dewatered in order to subsequently achieve a dry paper or cardboard web with presses and drying units. Fines and any additives used are washed out of the fiber network together with the filtrates. These fines are removed when the filtrate is cleaned using a curved sieve, disc filter, DAF (Dissolved Air Flotation) or similar units so that the filtrate can be used again. In the recent past it was found that the application of micro- or nanofibrillated cellulose (MFC or NFC) in or application to paper, cardboard or paperboard can change their properties in order to achieve improved mechanical properties, for example Changing the barrier properties (such as air permeability, oxygen or water vapor transmission or fat permeability) of the paper, board or paperboard, improving the optical properties (such as: gloss) as well as his/her water absorption. Microfibrillated or nanofibrillated cellulose is understood here to mean a cellulose produced by high-pressure homogenization or fine grinding of conventional pulps with or without the use of chemicals or enzymes or the like, or joint grinding with other grinding media, such as ground calcium carbonate, clay (kaolin) or other minerals becomes. The disadvantage of such a commercially produced micro- or nanofibrillated cellulose is that it can only be produced with a high expenditure of energy. In addition, the transport of MFC or NFC is not economically viable due to the usually low solids content in an aqueous suspension.

The application of micro- or nanofibrillated cellulose or microfibrillated cellulose fragments is, for example, in the document Beneventi et al. (2014); Industrial & Engineering Chemistry Research 53(27): 10982-10989, according to which such micro-

fibrillated cellulose fragments (MFC fragments) can be sprayed onto a fibrous web to produce composite materials which have better surface and barrier properties.

In the course of experiments it was found that the fibrous or cellulosic fines contained in pulp suspensions and various filtrates from the paper, cardboard, cardboard and pulp production can be used in a similar manner as micro- or nanofibrillated celluloses to the To change surface and barrier properties and the mechanical properties of paper, cardboard and paperboard.

DESCRIPTION OF THE INVENTION:

The present invention now aims to provide a method with which it is economically possible to further process the fibrous suspensions and/or filtrates containing cellulosic fines originating from paper production or pulp production and/or with further additives in this way enable the cellulosic fines contained therein, optionally together with other components of the filtrates, to be applied to paper, cardboard or paperboard in order to improve their surface, barrier and mechanical properties.

To solve this problem, the method according to the invention is essentially performed in such a way that at least the following steps are carried out.

a) Separation of the cellulosic fines from the filtrates with a size of less than 1200 μm, in particular less than 900 μm, preferably less than 600 μm, even more preferably less than 400 μm, particularly preferably less than 200 μm (measured according to ISO 160651 ) and any other additives that may be present,

[0008] b) optionally thickening the separated cellulosic fines of the same,

[0009] c) optionally mixing the separated cellulosic fines with other fines from paper, cardboard, paperboard or cellulose production, and/or micro- or nanofibrillated cellulose (MFC or NFC),

d) optionally forming an aqueous suspension from the fines or optionally the mixture of fines from additives originating from the manufacture of paper, cardboard or pasteboard,

e) optionally adding to the suspension of additives used in paper, cardboard, cardboard or pulp production, in particular native, derivatized or oxidatively treated starch, sizing agents, wet strength agents or other chemical additives or minerals such as. e.g. calcium carbonate or kaolin,

f) homogeneous application of the suspension formed on the surface of a paper, cardboard or cardboard web in an amount between 4 and 15 g atro / m * (atro = absolutely dry) of the solids in the suspension, the content of fines in the suspension is up to 100% of the dry matter contained in the suspension, preferably less than 90.0% of the dry matter contained in the suspension, and

[0013] g) drying of the paper, cardboard or cardboard and, if appropriate, simultaneous or subsequent pressing, calendering, coating with additives in a film or sump size press or a spraying process or other coating units used in paper, cardboard and cardboard production,

h) optionally repeating steps f) and g).

With such a process management, it is not only possible to separate cellulosic fines from a wide variety of filtrates and/or fibrous suspensions occurring in paper, cardboard, paperboard or pulp production, but these separated cellulosic fines or generally the separated fibrous components can directly and without having to go to another, locally different from the place where the cellulosic fines accumulate

another place of use, in particular another paper, cardboard, cardboard or pulp mill, again in one and the same manufacturing process or in the production of a different paper, cardboard or cardboard quality than that from whose filtrates they were taken, however be used at a later date. Surprisingly, it was found that by separating fines from the filtrates of the paper, cardboard, cardboard or pulp production in the further production process of paper and/or cardboard or cardboard and in the end product produced, in particular in the paper, cardboard or cardboard body no deterioration in the properties can be observed, although the separation of the cellulosic fines removed a non-negligible content of components from the fibrous suspensions or filtrates. Surprisingly, it has even been shown that with a method according to the invention, the effectiveness of additives remaining in the production process can even be increased by removing the fines from the fibrous suspension and the dewatering of the fibrous suspension can be improved.

In the prior art, cellulosic fines from filtrates from paper, cardboard, cardboard and pulp production are recycled into the paper, cardboard, cardboard or pulp production process, e.g. adding the fines before grinding or to the mixing tank after refining, or at other points in the paper production process before the headbox. However, it could be shown that adding the cellulosic fines to the production process again negatively affects the effectiveness of the necessary additives used, and that the presence of fines in the pulp suspension has a significantly negative impact on the dewatering of the same. For example, by removing part of the fines, as is done in the present invention, the freeness (according to ISO 5267 - 1:2004) from 20 °SR to 15 °SR) could be improved, with the tensile strength index of the paper samples with partial removal of the cellulosic fines to 103 - 106 N/mg (according to ISO 1924-3:2005 laboratory sheets according to ISO 52692:2004, basis weight according to ISO 536:2012) compared to a comparison without reduction of the fines, in which it was at 98 - 101 Nm/g (according to ISO 1924-3.2005 laboratory sheets according to ISO 52692:2004, basis weight according to ISO 536:2012) increased. Furthermore, due to the state-of-the-art recycling of fines from the filtrates, there is an increased need for retention aids as part of the chemical paper additives, which, depending on the paper, board and board qualities produced, of the fiber suspension in the approach flow of a paper, board and board machine ( up to immediately before the headbox) can be added. Common two-component retention aid systems consist of long-chain cationic and short-chain anionic polymers or the latter can optionally also be replaced by anionic microparticles and are mainly used to bind fibers and predominantly cellulosic fines and inorganic fillers on the wire section of a paper machine in the moist circulating paper. On the one hand, the specific chemical costs for such retention aid systems are not inconsiderable and, on the other hand, it is only rarely possible to achieve a target value of more than 90% total retention with them. The process management described in the method according to the invention makes it possible to prevent the above-described disadvantageous recycling of the cellulosic fines. By separating the fines and fillers from the fibrous stock suspensions and/or filtrates and applying them to a paper web, such as on the wire section of a paper machine, almost 100% retention can be achieved and thus the dosage of retention aids can be significantly reduced, which is a significant simplification of the procedure means.

By separating and, if necessary, mixing the separated cellulosic fines with other fines from other process steps of the manufacturing process or accompanying substances such as additives, chemicals or minerals from the paper, cardboard, cardboard or pulp production, it is possible to Provide surface coating material, which comes directly from the process and can be applied in turn to the paper, cardboard or paperboard surface in the same process after or during sheet formation. Depending on the type of additives contained in the various filtrates, originating from paper, cardboard or cardboard production or, if necessary, through the targeted addition of additives

ven, chemicals or minerals or the like, it is possible to carry out a selective surface treatment of the paper, board or paperboard with results which in this magnitude of improvement were completely unexpected for a person skilled in the art.

For example, it is possible to reduce the air permeability of paper, cardboard or cardboard (Gurley value according to ISO 5636-5:2003) by applying fines separated from the filtrates in such a way that the paper or cardboard is almost becomes airtight.

[0019] Fines as well as accompanying substances in the filtrates of the paper, cardboard, paperboard and pulp production have different properties. In use, these will lead to different results in the end product, namely the paper, board or cardboard, but these differences are not solely due to the subsequent division into three groups of fines, but are also due to the type of fines separated with the fines , mostly suspended or dissolved in the aqueous suspension. Fines or cellulose fibers are understood to mean the following materials in connection with the present invention: * Primary fines: A fines which preferably consists of particulate lignocellulosic substances and is preferably separated from an unground cellulose suspension. * Secondary fines: A fines that preferably results from a mechanical fiber treatment such as refining in pulp and paper, board, paperboard manufacture; * other types of fines such as chemicals, additives and minerals derived from the filtrate of paper, board, paperboard and pulp manufacturing.

Accompanying substances are understood here as meaning additives, chemicals or minerals that are also separated during filtration during the manufacture of paper, cardboard, cardboard and pulp, on the one hand because of their size or their solubility in the respective filtrate and on the other hand because of the fact that they are either chemically or physically bound to the fines.

The terms pulp and pulp are understood here to mean both pulp or pulp from chemical pulping and pulp from the various mechanical pulping processes and modifications (such as thermo-chemical pulp) of these processes that are common in the paper and pulp industry.

Among the additives, chemicals and minerals used in paper, cardboard, cardboard or pulp production is understood here: * calcium carbonate, * talc, * clay (kaolin) or * titanium dioxide or other minerals and optionally additives and chemicals such as * Sizing agents, e.g. * alkylated ketene dimers (AKD), * succinic anhydrides (ASA), * anionically and cationically modified resin and fatty acids * native and modified starches, such as * derivatized cationic, anionic and amphoteric starches, * oxo-additive treated starches * enzymatically treated starches , or * starches degraded by acid catalysis * retention aids + wet strength agents (epichlorohydrin, urea formaldehyde or similar) * surface-active substances (general surfactants) (anionic, cationic, non-ionic surfactants) * organic (cationic and anionic polymers) and inorganic (e.g. aluminum sulfate, polyaluminium chloride ) fixatives or any other in which paper, cardboard or similar chemical additives used in cardboard production

* Grease repellent chemicals: * Fluorine-based formulations * Perfluoroalkyl acids (PFAASs), such as perfluorocarboxylic acids (PFCAs) or perfluorosulfonic acids (PFSAs) * Fluorine-free formulations, e.g. based on starch derivatives, modified polymers, etc.

[0023] Filtrates from the production of paper, cardboard, paperboard and pulp are understood to mean, inter alia, the following process streams:

» Washing filtrates, e.g. from brown stock washing, bleaching, etc.:

* clear filtrate

* Turbid filtrate

* white water

According to a further development of the invention, the method is carried out in such a way that one or more of the fibrous suspensions and/or the filtrates of a paper machine, cardboard or paperboard machine or pulp manufacturing plant are discharged downstream of a sorting unit, such as a pressure screen, a curved screen or a Belt washers, which are used in the separation step for separating fines and any other additives present, is/are used. By using one or more of the fibrous suspensions and/or the filtrates of a paper machine or a pulp production plant downstream of a sorting unit, which are used in the separation step to separate fines and any other additives that may be present, it is possible on the one hand , to avoid the known negative or disadvantageous effects of the fines, such as on drainage or the amount of retention aid required, and on the other hand to obtain a paper, cardboard or cardboard product whose surface properties compared to conventionally treated surfaces of paper, cardboard and cardboard are significantly improved.

By, as corresponds to a development of the invention, the process is conducted in such a way that the fines are separated from the fibrous suspensions and/or filtrates in a single-stage or multi-stage separation and/or filtration process, in particular with a sorting unit or a disc filter or a flotation process, such as a DAF (Dissolved Air Flotation), it can be ensured that all fines of a certain size or thickness and any other additives that have accumulated on their surface are removed from the papermaking process and subsequently applied for application the paper surface are available. Processes such as a separation process using sorting units such as pressure screens such as disc filters or a flotation process such as the DAF have proven to be particularly favorable here, in which the fines can be made to float on the surface of the filtrate. Such a separation process not only recovers a very large part of the cellulosic fines contained in the filtrates and/or pulp suspensions, but also ensures that few or no additional resources have to be used to achieve a substantially complete or complete separation to ensure quantitative separation of the fines from the filtrates.

To ensure that when using the obtained from the fibrous suspensions and / or filtrates fines or optionally other additives on a paper, cardboard or. If the cardboard surface is not unnecessarily moistened and, in this way, not only do the process costs have to be increased, but the process control also has to be drastically changed, the process according to the invention is essentially carried out in such a way that a fines suspension is thickened up to a total solids content comprising cellulosic fines and possibly between 1 and 30% by weight, in particular 3 to 10% by weight, of additives originating from paper, cardboard or cardboard production. A thickening to a content of fines and optionally from the paper, cardboard or paperboard production additives to a content between 1 and 30 wt .-%, in particular 3 to 10 wt .-% in relation to the dry matter means that a relatively

suspension having a high content of cellulosic fines is applied to the surface of paper, cardboard or paperboard in order to be able to immediately provide the product with improved surface properties, in particular a significantly reduced air permeability.

In order to ensure that the surface finishing can be carried out with the method according to the invention in a single step and that two separate steps of applying fines and then auxiliaries or additives do not have to be carried out, the method according to the invention is essentially further developed to the effect that that the suspension formed from the cellulosic fines contains at least one additive selected from the group consisting of calcium carbonate, talc, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenylsuccinic anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention aids and retention aids or the like are added. By adding further additives to the suspension formed from the fines, the person skilled in the field of papermaking can already prepare a suspension in advance with which he can achieve the desired surface properties of a finished paper, board or cardboard that are most favorable for him. Needless to say, the cellulosic fines and the other additives cannot be applied several times at different points in the manufacture of paper, paperboard or cardboard, such as in the wire section and at a later point in time on the dry paper.

Desired surface properties are, for example, barrier properties such as defined air permeability and water vapor permeability, surface properties such as surface hydrophobicization or reduction in roughness, and mechanical properties such as a change in work absorption (TEA), an increase in flexural strength, but also optical properties such as and the The brightness or gloss of the paper can be significantly improved or increased in this way.

In this context, it is important to choose the exact ratio between the cellulosic fines and other additives so that the desired surface properties of the finished paper, board or cardboard can be achieved. According to a development of the invention, the ratio is essentially selected such that a ratio of fines to other additives is selected between 1:100 and 100:1, preferably 15:1, in particular 5:1. Even if a large and particularly broad area is covered by the present invention, it is clear to a person skilled in the art that, depending on the desired surface properties of the finished paper, cardboard or the finished cardboard, extremely different amounts of the individual components can be used for have to be used, so that if, for example, an air-impermeable paper is to be produced, the content of fines must be higher, whereas increasing a hydrophobic character of the paper, board or paperboard requires a larger amount of adjuvants.

Particularly good properties can be achieved if the process is carried out in such a way that the fines are in the form of fines impregnated with other additives originating from paper, cardboard or paperboard production, or in the form of adducts of the additives on the surface of the fines be used. With such a method, it is possible in particular to achieve a completely uniform distribution of both fines and other additives originating from paper, cardboard and cardboard production on the surface of paper or cardboard and a particularly homogeneous end product can thus be obtained. Such homogeneous end products not only show improved surface properties, but it can in particular be ensured that since the fine particles are impregnated with the other additives or are present as adducts with these substances, at least both products can always be applied in a specific proportion to one another and thus particularly evenly the surface can be distributed.

In order to subsequently apply the fines separated from the various filtrates and/or fibrous stock suspensions of paper, cardboard or cardboard production to the surface of paper, cardboard or cardboard, it has proven advantageous to adjust the pH of the suspension adjusted, depending on the desired surface properties different pH values of the suspension can be adjusted.

According to the invention, pH values for a suspension to be applied to paper, cardboard or paperboard surfaces of 4 to 9 have proven to be preferred.

According to the invention, surface coating processes such as surface coating of a paper web having a dry content between 2 and 100% Cardboard or paperboard web such as found in a film press or sump press or a spray process. In such a coating process, the wet paper web already has a structure and the most important parameters that can be set by the paper machine are already set, such as the basis weight of a paper, but at this point the surface properties of the paper can be adjusted particularly efficiently to the final requirements.

By carrying out the method according to the invention in such a way that, after the surface coating method, a surface finishing method, such as calendering, pressing, drying on a polished, machine smoothed Yankee cylinder, is carried out in a coating system, such as a film or sump size press, rollers or smoothing, succeeds it is to further improve the surface improvements achieved by surface coating with the help of the fines separated from the fibrous suspensions and/or filtrates of the paper, cardboard or paperboard production, for example by even greater smoothness, air impermeability and the like being achieved by the surface finishing process .

The invention further also relates to a paper, board or cardboard produced by a method according to the invention. Such paper, such cardboard or such cardboard are essentially characterized in that the paper, cardboard or cardboard has a surface coating which is between at least 0.5 g atro/m? and 30 g atro/m?, in particular 4 g atro/m? and 15 g atro/m? Contains fines and optionally further additives. By producing paper, cardboard or paperboard that has a surface coating that contains at least 0.5 g atro/m* or a maximum of 30 g atro/m* fines and, if necessary, other additives in the coating, it is possible to provide a paper, board and paperboard which has significantly improved surface properties compared to conventionally manufactured products. For example, an almost completely air-impermeable cardboard or an air-impermeable paper or an air-impermeable cardboard can be provided, a paper, cardboard with improved gloss, improved moisture resistance or increased smoothness can be obtained, with all of these properties always compared to paper , paperboard or paperboard produced from a pulp suspension in which the fines have not been stripped off in the course of the process and have not been reapplied as a surface coating material in the manufacturing process, as in the process according to the present invention .

According to a development of the invention, such a paper is designed in such a way that the surface coating consists of a mixture of fines, in particular a mixture of fines and additives contained in the filtrates from the paper, cardboard, cardboard or pulp production. Such a paper differs from conventionally produced papers essentially in that additives or fines originating from the process are used almost exclusively for its surface finish and thus not only a significant cost saving but in particular a saving of raw materials can be achieved with such a paper.

[0037] In order to determine the surface properties of such paper, cardboard or such

To be able to adapt the cardboard exactly to the following requirements, the paper, the cardboard or the cardboard is further developed in such a way that the surface coating, in addition to fines, the mixture of fines and the additives originating from filtrates of the paper, cardboard, cardboard or pulp production, contains other additives added before coating. In particular, by adding other additives before coating, it is possible to influence the surface properties of the paper in a targeted manner, in addition to the positive effects of the fines and the additives originating from production, and thus to provide paper qualities or cardboard qualities that exactly meet the requirements of an end user .

The amounts of the other additives in the surface coating are in the range from 0.5% by weight to 99% by weight of the dry matter of the coating suspension, which makes it possible to produce paper that is precisely tailored to the needs of the end consumer and at the same time inexpensive , cartons or cardboard to provide.

The invention is explained in more detail below with reference to drawings and exemplary embodiments. In these shows

Figure 1 is a schematic representation of a flow sheet of an integrated pulp, paper, board or paperboard mill showing schematically the possibility of separating fines and their final application.

In this representation, an integrated pulp, paper, board or paperboard manufacturing plant is indicated by the broken peripheral line 1, which integrated paper and pulp manufacturing plant is divided into two separate plants, such as a pulp manufacturing plant, but which also includes a paper , board or paperboard manufacturing plant, represented by a further dashed outline 2, hereinafter referred to as pulp manufacturing plant 2, and a paper, board or paperboard manufacturing plant, shown by a further dashed outline 3 is, is divided.

In the pulp manufacturing plant 2, a non-bleached fibrous feedstock or a fibrous material or a filtrate is applied at 5 to a separating device 6, which can be, for example, a filtration, a pressure screen, a disc filtration, a flotation plant or a sedimentation plant can. Cellulosic fines are drawn off at 7 in this separating device 6 and subsequently optionally subjected to thickening 8, for example by flotation. Clear filtrate drawn off from thickening 8 , consisting essentially of water or water containing soluble chemicals, is drawn off at 9 .

In the separating device 6, not only cellulosic fines are removed from unbleached starting material, but in particular the unbleached starting material or the fibrous material or the filtrate is freed from the cellulosic fines that are not desired in pulp production, and the starting material thus freed is removed at 10 and, for example, bleaching (not shown).

The suspension containing fines is either passed through the thickening section 8 and then drawn off from this thickening section 8 and either applied directly to the paper machine 4 via line 11 and used as a surface finish, or optionally with other cellulosic or fibrous materials fed in via line 18 Fines, additives and chemicals that may be included from papermaking mixed at 12.

Alternatively, the process can also be carried out bypassing thickening 8, in which case the fines drawn off at 7 are further treated via line 11, as described above.

The fines obtained from the pulp, paper, board or board manufacturing plant can be applied to the pulp in the paper, board or board machine 4 . The filtrate from the dewatering of the paper, cardboard or cardboard machine 4 is

Device 13 in turn fed to a separation 14, in which separation 14 fines are separated from the clear filtrate. This separation can in turn be effected by flotation or, for example, with disk filters. The clear filtrate obtained in this separation can either be fed directly to the paper machine 4 via line 15 or, if necessary, mixed with another clear filtrate 16, which can come from an optional thickener 17, and then the paper, cardboard or Cardboard machine 4 are supplied. The cellulosic fines further concentrated in the further thickening 17 are mixed with the cellulosic fines originating from the pulp production plant 2 at 12 and then fed to the paper, cardboard or cardboard machine 4 via line 11 .

With such a process, it is possible to separate cellulosic or fibrous fines from this filtration from the filtrates and/or fibrous suspensions from the paper, cardboard and/or pulp production, to concentrate the material and use it as a surface finishing material on an already produced paper - to apply cardboard or cardboard web, which not only makes it possible to significantly improve the surface properties of the paper, cardboard or cardboard, but in particular it can be achieved that the dosage of retention aids can be greatly reduced or avoided altogether and the negative influence continues of fines on dewatering in papermaking can be avoided.

The invention is further explained in more detail using exemplary embodiments. Example 1: Mechanical Paper Properties

After application of the fines obtained from papermaking (solids content >0.3% by weight of fines in water) to the moist base paper, the influence on the mechanical paper properties was examined. It can be clearly seen that the application of fines - regardless of the application method - has a positive influence on the mechanical paper properties. The application of fines causes a densification of the fiber network and leads to more fiber-fine bonds, which have positive effects on important mechanical properties such as tensile strength, stiffness, TEA (Tensile energy absorption). An increase in the mechanical paper properties can be demonstrated at application quantities of approx. 1 g/m* and above, with the improvements in the mechanical paper properties increasing with the amount of fines applied.

The following examples (1) to (IV) were each applied with a fines weight of 3 g atro / m? on a sheet of paper with a mass per unit area of 100 g/m”.

In example (I) an improvement in the mechanical paper properties by around 10% with a fines coating weight of 3 g atro/m? on a 100 g/m? paper sheet reached.

A) Tensile strength - measured according to ISO 1924-3-2005

a.) Base paper - untreated samples -> 7.5 kN/m

b.) Paper + applied fines -> 8.2 kN/m

B. Tensile Energy Absorption - measured according to ISO 1924-3-2005 a.) Base paper - untreated samples -> 165 J/m?

b.) Paper + applied fines -> 180 J/m?

C) Stiffness - measured according to ISO 1924-3-2005

a.) Base paper - untreated samples -> 775 kN/m

b.) Paper + applied fines 850 kN/m

Papers treated with fines also have high grease resistance. Depending on the type and application, a KIT value (test for fat resistance with KIT values from 1 - no fat barrier to 12 - excellent fat barrier) to 11 is possible.

In example (II), the fat resistance was measured (KIT value measured according to T559-cm2012)

[0055] Base paper - fines-free, untreated > KIT value = 1 [0056] Paper surface-treated with fines > KIT value = 11

Another advantage is that a closed paper surface is possible through the use of the fines. This was characterized using Bendtsen air permeability (unit: milliliters of air per minute).

In example (III), air permeability was measured according to Bendtsen (DIN 53120-1-2018) Base paper - fines-free, untreated > 222 ml/min Paper treated with fines > 0 ml/min (dense)

Fines also improve the water vapor transmission (WDT, unit: mass of water vapor per m? in 24 hours) of the paper and these can serve as a water vapor barrier or to improve the water vapor transmission of various types of paper. A low WDT is particularly relevant for packaging paper and can be positively influenced by the fines.

In example (IV), the water vapor transmission was measured according to ISO 2528-2017. Base paper - free of fines, untreated >WDT=425 g/m**24h

Paper treated with fines > WDT = 170 g/m**24h

Example 2. Increase in the effectiveness of additives, savings in retention aids.

If fines from a separation/thickening step are not "recycled" as usual, i.e. returned to the machine container after grinding, where, among other things, the additives are metered, there are advantages of almost 100% retention and a Higher effectiveness of the metered additives, such as cationic starch to increase strength The mode of action is based on the fact that fines have a high specific surface area and anionic charge and thus bind the cationic starch preferentially, which means that the increase in tensile strength of the end product is less. The process management according to the invention reduces the proportion of fines in the machine container and thus there is the possibility of obtaining comparable paper properties even with a smaller dosing quantity of starch or another cationic synthetic or natural polymer.

Fines were removed from an industrially ground pulp (low-consistency beating to a degree of freeness of 20° SR), as a result of which the degree of freeness could be reduced to 15° SR (measured according to ISO 5267-1:1999). Drag also dropped noticeably (from 15 seconds to under 10 seconds). Surprisingly, the tensile strength of laboratory sheets (according to ISO 19243:2005, laboratory sheets according to ISO 5269-2:2004, basis weight according to ISO 536:2012) fell only slightly as a result of the reduced fines content. The pulp was diluted with the filtrate from a paper machine to 0.5% consistency and the pH was adjusted to pH 6.8 with aluminum sulfate. Dosing series with cationized starch (2 similar types) were then carried out such that 10 kg starch/t pulp, as well as 15 kg/t and 20 kg/t were dosed. Laboratory sheets with 80 g/m? manufactured. The handsheets were stored overnight at 23° C. and 50% rel. Humidity conditioned and tested.

The results of the tests are shown in Table 1

Example 3. After the application or the application of the fines (coating weight> 1 g atro / m®) on the dry paper sheet was a reduction in air permeability (measured with Gurley ISO 5636-3-2013-11) and the Bendtsen -Roughness (measured according to ISO 8791 -22013-9) achieved.

Sample 1. Paper without fines - Gurley LD = 15 s (seconds) Paper treated with fines - Gurley LD = 126 s

Sample 2. Paper without fines - Bendtsen roughness = 1575 ml/min Paper treated with fines - Bendtsen roughness = 673 ml/min

From the ratio of tensile strength and Gurley air resistance, which is significantly improved in the process compared to the prior art, it can be seen that separating the cellulosic fines from the filtrates and/or fibrous suspensions of a paper, cardboard, Cardboard or pulp manufacturing plant and the subsequent application of the same to the paper surface, a substantial improvement in the properties of the paper, paperboard or cardboard can be achieved.

Claims (14)

patent claims 1. A process for separating fines from fibrous stock suspensions and/or filtrates of a paper, cardboard, cardboard or pulp manufacturing plant and for reapplying the separated fines to a surface of paper, cardboard or cardboard, characterized in that at least the following Steps are carried out a) Separation of the cellulosic fines from the pulp suspension and / or filter rates with a size of less than 1200 μm, in particular less than 900 μm, preferably less than 600 μm, even more preferably less than 400 μm, particularly preferably less than 200 μm (measured according to ISO 16065-1) and any other additives present, b) optionally thickening the separated cellulosic fines of the same, c) optionally mixing the separated cellulosic fines with other fines from paper, cardboard, paperboard or cellulose production, and/or micro- or nanofibrillated cellulose (MFC or NFC), d) optionally forming an aqueous suspension from the fines or, optionally, the mixture of fines from additives originating from the manufacture of paper, cardboard or paperboard, e) optionally adding to the suspension additives used in paper, board, cardboard or pulp production, in particular native, derivatized or oxidatively treated starch, sizing agents, wet strength agents or other chemical additives or minerals such as e.g. calcium carbonate or kaolin, f) homogeneous application of the suspension formed to the surface of a web of paper, cardboard or paperboard in an amount between 4 and 15 g atro/m? the solids present in the suspension, the content of fines in the suspension being up to 100% of the dry matter contained in the suspension, preferably less than 90.0% of the dry matter contained in the suspension, and g) Drying of the paper, cardboard or paperboard and, if necessary, simultaneous or subsequent pressing, calendering, coating with additives in a film or sump size press or a spraying process or other coating units used in paper, cardboard and paperboard production, h) optionally repeating steps f) and g). 2. The method according to claim 1, characterized in that one or more of the fibrous suspensions and/or the filtrates of a paper machine, cardboard or paperboard machine or pulp manufacturing plant, after a sorting unit, such as a pressure screen, a curved screen or a belt washer , which are used in the separation step for separating fines and any other additives present, is/are used. 3. The method according to claim 1 or 2, characterized in that the separation of the fines from the fibrous suspensions and/or filtrates in a single-stage or multi-stage filtration and flotation process, in particular with a disc filter or a flotation process such as a DAF (Dissolved Air Flotation ) is carried out. 4. The method according to claim 1, 2 or 3, characterized in that the thickening up to a total solids content comprising fines and any additives originating from the paper, cardboard or paperboard production between 1 and 30 wt.%, in particular 3 to 10 wt. -% is carried out. 5. The method according to any one of claims 1 to 4, characterized in that the suspension formed from the fines as further additives for the surface treatment of paper, cardboard or cardboard at least one additive selected from the group consisting of calcium carbonate, talc, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenylsuccinic anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention aids are added. 6. The method according to claim 5, characterized in that a ratio of fines to other additives between 1:100 and 100:1, preferably 15:1, in particular 5:1 is chosen. 7. The method according to claim 5 or 6, characterized in that the fines are used as fines impregnated with the other additives originating from the paper, cardboard or cardboard production or as adducts of the other additives on the surface of the fines. 8. The method according to any one of claims 1 to 7, characterized in that a pH of the suspension to be applied to a paper, cardboard or cellulose surface between pH 4 and pH 9 is selected. 9. The method according to any one of claims 1 to 8, characterized in that the surface coating method used is a surface coating of a paper web, cardboard or cardboard web having a dry content between 2 and 100%, such as with a film press or sump press or a spraying process. 10. The method according to any one of claims 1 to 9, characterized in that after the surface coating process, a surface finishing process, such as calendering, pressing, drying on a polished, machine smoothed Yankee cylinder, a coating system, such as a film or sump size press, rolling or smoothing is carried out . 11. Paper, cardboard or cardboard produced by a method according to one of claims 1 to 10, characterized in that the paper, cardboard or cardboard has a surface coating which is between at least 4 g atro/m* and 15 g atro/m? Contains fines and optionally further additives. 12. Paper, cardboard or cardboard according to claim 11, characterized in that the surface coating has a mixture of fines, in particular a mixture of fines and additives contained in the filtrates from the paper, cardboard, cardboard or pulp production. 13. Paper, cardboard or cardboard according to claim 11 or 12, characterized in that the surface coating contains other additives added before the coating in addition to fines, the mixture of fines and the additives originating from filtrates of the paper, cardboard, cardboard or pulp production . 14. Paper, cardboard or cardboard according to claim 11, 12 or 13, characterized in that the further additives of the surface coating are contained in an amount of 0.5% by weight to 99% by weight of the dry matter of the coating. 1 sheet of drawings